1. Field of the Invention
This invention relates generally to systems for controlling chemical processes, and more particularly, to a chemical analyzer system that performs several basic functions, specifically sampling, analysis, mixing, replenishment, and cleanup, and further including the functions of performing diagnostics, auto-calibration, and calculations. In addition, the invention relates to a system of humidifying nitrogen gas to a predetermined relative humidity level, and to calibration of an on-line pH sensor using an off-line pH sensor.
2. Description of the Related Art
A chemical management system, such as a system that controls a plating process is required to perform a number of functions, not all of which have been successfully implemented in the prior art. For example, in a chemical system that employs a NiFe plating bath, there is a need that the NiFe plating bath be ready for use on demand. A system that manages the plating bath, preferably should prepare and hold a new plating bath, and measure and control the bath chemistry. The temperature of the bath should be controlled and adjustments to the quantity of fluid in the bath should be effected by replenishment as evaporation occurs. In addition, it is preferred that the bath be aged by performing dummy plating.
In a manufacturing environment, there is a need to distribute the plating solution to tanks in the manufacturing area. Particles should be filtered out and a continuous flow of solution should be achieved in the interconnecting tubing.
In some manufacturing environments, multiple sets of holding and mixing tanks are provided at predetermined locations in the manufacturing area. In some cases, each set of mixing and holding tanks has a respectively associated chemistry. There is a need for an arrangement that reduces the duplicated components in a chemical control system that would control the operation of such plural tank sites.
As previously stated, at each such site there may provided a holding tank and a mixing tank. The holding tank stores plating solution that is in a condition ready to be used. The mixing tank, on the other hand, is used to make up plating solution and for dummy plating. Of course, each such tank is constructed to be chemically inert with respect to the chemistry of the plating solution. Materials that are known to be suitable for this purpose are Teflon® materials and equivalents.
There is additionally a need for a chemical control system that permits nitrogen gas to occupy the space above the liquid surfaces in the tanks. The nitrogen gas forms a blanket that prevents oxidation of the chemistry, and when properly humidified, an increase in the amount of the solution, as results from known fog humidifiers. Additionally, the properly humidified nitrogen blanket reduces dehydration of the plating solution, which would result in elevated concentration thereof.
A number of system parameters must be monitored and controlled. These included, specifically in a NiFe plating environment, the respective concentrations of Ni and Fe. In addition, the pH of the solution, as well as its density and temperature need to be controlled to within predetermined ranges. Moreover, the dummy plating system, including the plating schedule and the current used therein, must be controlled as must the Fe concentrate during dummy plating.
In addition to the foregoing, there is a need for a sensor system that provides accurate information relative to the quantity of a fluid in a tank. External proximity sensors, for example, can be falsely activated by a light crystalline tank wall build up or certain changes in environmental conditions such as humidity. Sensors used in industrial applications should not be affected by tank wall build up, foaming, stirring, temperature, humidity, RF interference, or electrical noise. The sensor system should not require adjustment after installation. Also, it should provide a continuous measurement along the full depth of the tank. Such a measurement capability allows an immediate inventory of contents that is used by other portions of the system, illustratively in accordance with control software, for continuous monitoring of pump performance and for confirmation of flow sensor accuracy.